we are building 3 docker images and pushing to 3 ECS fargate services. The docker images build in parallel, but replacing the task definitions run in series. i am wondering if this is default behavior or if there is a way to parallelize the fargate task deployments as well

If there's no dependency from one definition to the next, they should happen in parallel. Have you checked that there's no chain of resource dependencies between the definitions?

mmm i dont believe so, but is there a way to debug like a dependecy tree or something to make sure?